The invention relates to a regenerative thermoacoustic energy converter (TAEC), comprising an acoustic or mechanical-acoustic resonator circuit and a regenerator clamped between two heat exchangers.
Generally, a TAEC is a closed system in which in a thermodynamic circle process heat and acoustic energy, i.e. gas pressure oscillations, are transformed into each other. TAECs have a number of properties, which make them very suitable as heat pump, e.g. for refrigeration or heating, or as engine for driving pumps or generating electrical power. The number of moving parts in systems that are based on TAEC is limited and in principle no lubrication is needed. The construction is simple and offers a large freedom of implementation allowing the manufacturing and maintenance costs to be low. TAECs are environmentally friendly: instead of poisonous or ozone layer damaging substances, air or a noble gas can be used as the heat transfer medium. The temperature range of operation is large, thus allowing a large number of applications. Owing to the closed system, the external noise production is low; besides, the frequency spectrum is limited, so that, if necessary, adequate measures can be taken to minimise noise nuisance and vibrations.
A regenerative TAEC comprises an acoustic or acoustic-mechanical resonance circuit, in which a gas is present, as well as two heat exchangers, on both sides of a "regenerator" of a pourous material with good heat exchange properties. Assuming that the gas, having a certain temperature, is already in oscillation, heat is moved, under the influence of the acoustic wave, from the one heat exchanger, the entrance heat exchanger, to the other, the exit heat exchanger.
A TAEC can be used as a heat pump or as an engine. In the former case mechanical energy is added, by which the gas is brought into oscillation by means of e.g. a membrane, bellows or a free piston construction; by means of the oscillating gas heat is then "pumped" from the one heat exchanger to the other. In the latter case, as an engine, heat is supplied to the one heat exchanger and heat is drained at the other, whereby oscillation of the gas column is kept up; the gas movement can be coupled out as useful energy through the membrane. Said heat pump can also be driven directly without intervention of a membrane and E/M converter by said engine, by which a heat pumping system driven by heat comes about without any moving parts at all. From the patents referred to hereafter, TAECs are known as "pulse tubes", characterized by a so-called thermo-acoustic stack with a limited heat exchange and heat exchangers with a length greater than or equal to the local extension amplitude of the gas. In order to enlarge the refrigerating capacity, according to said patent, the pulse tube is provided with one or more "orifices", exit openings or bypasses of small diameter, connected to a buffer. As a consequence of such a controllable leak", the phase shift between gas pressure and velocity at the location of the stack is reduced and the impedance is lowered, thus increasing the heat pumping capacity. In fact, there is question of an RC network. True enough the capacity is increased by such an RC network, but because of energy dissipation in the resistive component of the network (orifice), the net efficiency is negatively affected.
From patent applications referred to hereafter regenerative TAECs are known as "travelling wave heat engines", characterised by a regenerator included in a travelling wave resonator. The value of the impedance at the location of the regenerator in a travelling wave resonator is relatively low, causing the influence of the flow resistance in the regenerator to be dominant. The efficiency is hereby adversely affected.
The present invention aims at increasing the capacity of a TAEC in a way wherein the efficiency loss observed in said exemplary embodiments does not or hardly take place and the net efficiency is much more favourable then in known TAECs.